The use of polyalpha-olefins or copolymers thereof to reduce the drag of a hydrocarbon flowing through a conduit, and hence the energy requirements for such fluid hydrocarbon transportation, is well known. These drag reducing agents or DRAs have taken various forms, including slurries of ground polymer particulates and gels. A problem generally experienced with simply grinding the polyalpha-olefins (PAOs) is that the particles will “cold flow” or stick together after a relatively short time, thus making it impossible to place the PAO in the hydrocarbon in a form that will dissolve or otherwise mix with the hydrocarbon in an efficient manner. Further, the grinding process irreversibly degrades the polymer, thereby reducing the drag reduction efficiency of the polymer.
One common solution to preventing cold flow is to coat the ground polymer particles with an anti-agglomerating agent. Cryogenic grinding of the polymers to produce the particles prior to or simultaneously with coating with an anti-agglomerating agent has also been used. However, some powdered or particulate DRA slurries require special equipment for preparation, storage and injection into a conduit to ensure that the DRA is completely dissolved in the hydrocarbon stream.
Gel or solution DRAs have also been tried in the past. However, these drag reducing gels also demand specialized injection equipment, as well as pressurized delivery systems. They are also limited to about 10% polymer as a maximum concentration in a carrier fluid due to the high solution viscosity of these DRAs. Thus, transportation costs of the DRA are considerable, since up to about 90% of the volume being transported and handled is inert material.
Further, as noted, some polymeric DRAs additionally suffer from the problem that the high molecular weight polymer molecules can be irreversibly degraded (reduced in size and thus effectiveness) when subjected to conditions of high shear, such as when they pass through a pump. Additionally, some polymeric DRAs can cause undesirable changes in emulsion or fluid quality, or cause foaming problems when used to reduce the drag of multiphase liquids.
Surfactants, such as quaternary ammonium salt cationic surfactants, are known drag reducing agents in aqueous (non-hydrocarbon) systems and have the advantage over polymeric DRAs in that they do not degrade irreversibly when sheared. In contrast, flow-induced structures in surfactant solutions are reversible. However, the use of significant amounts of a surfactant in reducing the drag of mixed flow fluids such as the mixture of hydrocarbons and water can have the undesired side effect of creating a tight emulsion during flow that must be resolved downstream. Other drag reducing agents have tendencies to form deleterious emulsions, or perpetuate emulsions already formed.
Further, water soluble polymers have been used to increase water throughput in single phase processes such as water-floods for enhanced oil recovery. However, unlike such single phase systems, most oil and gas production systems contain multiple phases (e.g., water/oil, water/oil/gas). These multiphase systems are often limited in their production capacity due to friction-related or flow-regime-related losses. In subsea multiphase pipelines, delivering active materials that can increase production is made difficult by the rigorous requirements that must be met by the chemical that is to be delivered. That is, products must not be too viscous to be pumped or be susceptible to physical separation that can lead to blockages in the umbilical conduits used to deliver chemicals. It is known that conventional water soluble emulsion polymers have viscosities that are too high for umbilical injection and they tend to phase separate during storage.
Thus, it would be desirable if a drag reducing agent could be developed which rapidly dissolves in the flowing hydrocarbon mixture or emulsion, which could minimize or eliminate the need for special equipment for preparation and incorporation of the agent into the hydrocarbon mixture or emulsion, and which could avoid shear degradation during its production and injection. It would also be desirable to find a water-soluble drag reducing agent that has a relatively low viscosity and which can be readily pumped, and which is stable during storage.